The desire for a practical high-moisture, yet shelf-stable pet food has been discussed in the prior art for years. The standard, however, for commercial products has remained intermediate moisture products of the type discussed by Burgess et al in U.S. Pat. No. 3,202,514. These products typically have moisture contents of less than 30% and have sufficient amounts of solids to reduce the water activity to below about 0.88. The soluble solids will typically include salt, sugars and polyhydric alcohols. In addition, antimicrobials, such as sorbic acid and its edible salts, are typically employed to protect the food against attack by molds and other organisms not controlled by low water activity. This is especially important where heating followed by condensation, or other such changes which may occur as the normal consequence of commercial shipping and storage during which the product may be subjected to extremes of temperature and humidity, can cause a localized imbalance in the water activity in the product. Some patents, such as U.S. Pat. No. 3,658,548 to Haas have described other antimicrobials for use in products of this type in place of the sorbates. Haas discloses that caproic (hexanoic) and caprylic (octanoic) acids are effective antimycotics at levels of 0.3 percent or less in products containing from 15 to 30 percent moisture and a level of soluble solids at least equal to the level of moisture. In U.S. Pat. No. 4,002,775, Kabara identifies other food-grade antimicrobials based on fatty acids.
In one departure from the conventionally lower-moisture products, Bernotavicz, in U.S. Pat. No. 3,985,904 describes what is said to be a high-moisture, shelf stable product. This product contains at least 50% cooked meat and greater than 50 percent moisture. It has a water activity of greater than 0.90 and further contains from 1 to 35 percent gelatinized starch, a low level of an antimycotic, and from 1.7 to 3.8 percent of an acid which maintains the pH within the range of from 3.9 to 5.5. However, when the product of that invention was tested, it did not prove reliably stable.
Also, Ernst et al disclose a high-moisture pet food in U.S. Pat. No. 4,158,706, which is said to be stable against microbial attack without pasteurization when packaged in transparent, flexible containers. The food is disclosed as containing at least 50 percent water, a binder and from 0.5 to 5.0 percent of an acid selected from the group consisting of succinic acid, pyruvic acid, and fumaric acid.